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Date:   Wed, 1 Nov 2023 08:41:39 +0100
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Subject: Re: [PATCH] refscale: Optimize process_durations()
To:     paulmck@kernel.org
Cc:     Davidlohr Bueso <dave@stgolabs.net>,
        Josh Triplett <josh@joshtriplett.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Neeraj Upadhyay <quic_neeraju@quicinc.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Zqiang <qiang.zhang1211@gmail.com>, linux-kernel@vger.kernel.org,
        kernel-janitors@vger.kernel.org, rcu@vger.kernel.org,
        Kees Cook <keescook@chromium.org>
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From:   Christophe JAILLET <christophe.jaillet@wanadoo.fr>
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Le 31/10/2023 à 23:47, Paul E. McKenney a écrit :
> On Tue, Oct 31, 2023 at 11:21:14AM -0700, Paul E. McKenney wrote:
>> On Mon, Oct 30, 2023 at 09:55:16AM -0700, Davidlohr Bueso wrote:
>>> On Sat, 28 Oct 2023, Christophe JAILLET wrote:
>>>
>>>> process_durations() is not a hot path, but there is no good reason to
>>>> iterate over and over the data already in 'buf'.
>>>>
>>>> Using a seq_buf saves some useless strcat() and the need of a temp buffer.
>>>> Data is written directly at the correct place.
>>>
>>> Makes sense.
>>>
>>> Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
>>
>> Queued and pushed, thank you all!
> 
> But an allmodconfig build complains about seq_buf_putc() being undefined,
> that is, not exported.  I suspect that other seq_buf_*() functions in
> this patch might also be complained about.
> 
> I am dropping this for the moment.  Please make it pass an allmodconfig
> build so that I can pull it in again.  Please see below for the commit.
> 
> 							Thanx, Paul
> 

Ouch!

seq_buf_init(), seq_buf_terminate(), seq_buf_clear() are inlined 
functions in a .h file, so shouldn't be a problem.

seq_buf_printf() is exported, but seq_buf_putc() is not!
Really odd to me.

Kees Cook (added in cc) suggests to use this API (see [1]) to avoid some 
potential issues and ease the management of NULL terminated strings in 
buffers. (#LinuxHardening).

I'll propose to add the missing EXPORT_SYMBOL_GPL.

CJ

[1]: https://lore.kernel.org/all/202310241629.0A4206316F@keescook/